Shane, that’s an interesting question and turns out to be a difficult one to answer well. Depending upon the source, the count of named of dinosaurs varies from 1000 to 1400 species. However, it has become apparent in recent years that probably only two-thirds of these types are real. The decrease is due to: 1) more and better dinosaur fossils being found, and 2) a better understanding of the biology of dinosaurs. In early studies, some dinosaurs were named on the basis of very few fossil remains, such as part of a single individual or even a few bones, and these sometimes poorly preserved. Later, studies have shown that these fossils actually represented other, already named, types. An example of this is the Brontosaurus, which was later shown to be the previously named Apatosaurus.

Our increasing knowledge of dinosaur biology has also caused a rethinking of what it is to be a species (that is, kind) of dinosaur. In some cases there may be a significant difference in structure between males and females of the same species ("sexual dimorphism"), so that the two sexes are first named as separate species. In addition, form may change during development, with juvenile dinosaurs looking quite different from their mature adult forms. This has resulted in several current debates. In addition, it has for example been proposed that the familiar frilled horned dinosaur Triceratops is actually an immature form of the larger Torosaurus.

Even given these complications in recognizing what a kind/species of dinosaur is, it seems likely that the number of valid dinosaur species will continue to increase. New discoveries are made every year as new previously unexplored sites (such as in Argentina and China) are studied. Finally, I should note that it is generally accepted that the birds are direct descendants of the dinosaurs, so you may be watching a "dinosaur" hopping around on your lawn right now.